More than one third of the medicinal drugs currently on the market contain active ingredients, which nature has made available, that is, they were isolated from plants or microorganisms or, at the very least, modified on this basis.
In spite of this relatively large number of biological active substance, which nature has made available, worldwide efforts have, until now, been concentrated more on the chemical synthesis than on the so-called pool of natural products. In recent years, however, new active ingredients were discovered, which were created by nature and, as a result, natural products chemistry or natural products biochtechnology has therefore experienced a renaissance.
At the same time, with the discovery or production of new active ingredients, there was a rapid development in the sector of test system capacities. Whereas such biological assays for finding potentially new active ingredients some years ago required a few 100 mg of substance and, with that, only a few throughputs of tests per year were possible, the situation at the present time is basically different. As a result of test designs, which assume, for example, the inhibition of a specific enzyme as a measure of the biological activity, miniaturized automatic test machine can be realized, with which a million substances per year can be investigated, while at the same time little substance is consumed. The presence of these enormous test system capacities meets the requirements of natural products research, because frequently, until it is possible to detect a special biological activity, only a few milligrams of pure natural products, isolated from plants or microbial fermentations, are available.
Although a large number of natural products is already known, it must be assumed that nature has on hand a much larger number of substances, which until now have not been known, so that a high throughput screening of a large number of crude plant and microbial extracts cannot be avoided.
However, the testing of natural products requires a protracted procedure of preliminary purification, preliminary separation, intermediate purification and final purification, which must always be interrupted once again by testing for biological activity. This procedure requires much time, a large effort by personnel and a large logistic expenditure and moreover frequently leads to chemical substances, which are not worthwhile following up further.
In view of the cost pressures, which are carried over from the Public Health Service into the researching facilities, such time losses lead to constantly greater disadvantages for research and development, based on natural products research. Plant and microbial extracts are highly complex mixtures of substances. They contain extremely polar as well as nonpolar materials in large numbers. Basically, the separation of these mixture is possible with chromatographic methods. However, the time required for the separation with previously known chromatographic equipment, such as HPLC equipment, is unjustifiably high.
In the BEO 1994 annual report of the Bundesministerium fur Bildung, Wissenschaft, Forschung und Technology (Federal Ministry for Education, Science, Research and Technology) pages 413 and 414, HPLC equipment for the isolation of natural products is described, which is intended to fractionate plant and microbial extracts coarsely and finely.
The equipment has the following disadvantages:
The fraction-collecting columns, named were, are connected over 12-way valves, the use of which for preparative applications is very expensive. The frequency of the switching required here leads to more rapid wear of components and seals. PA1 A variable use, corresponding to the mixture that is to be separated, by increasing or decreasing the number of columns, is not possible, that is, because of this design, a modular construction of the equipment is not possible. PA1 The large number of fraction-collecting columns leads to a long running time and to a high consumption of solvents. PA1 An inexpensive and time-saving roll-over operation is not possible. PA1 The isocratic separation in the second separation step, which is provided for here, also leads to a disadvantageous extension of the running time.